1. Field of the Invention
This invention relates to infinite speed transmissions with power transferred from a drive shaft to a driven shaft by a ring or belt nipped between them.
2. Background Art
Infinite speed drives are known in many varieties. The discussion here shall focus on those in which two cones, or a cone and a cylinder (which is a cone of 0.degree.), oppose each other. The axes of both cones are in a common plane. The two cones have two parallel lines between them at their closest point and the power is transferred by a ring or belt which encompasses one of the cones and is nipped between them.
In any friction drive, loss through slippage is one of the main disadvantages over a drive in which gears mesh distinctly. Slippage can be reduced or overcome by increasing contact pressure, but often at the cost of jamming (which hinders shifting), stalling, or excessive bearing wear.
An infinite speed drive, or continuously variable transmission (CVT), has the conflicting goals of maximizing rotative friction, which is necessary for transmitting power, while minimizing lateral friction, lateral friction being detrimental to shifting. The heavier the load on the drive, the more pressure must be applied and this will amount to more friction, both rotative and lateral. The design of the present invention addresses the problem of undesirable lateral friction, which inevitably comes with the high pressure needed for rotative friction.
In friction drives involving cone-shaped shafts, there is also a problem caused by the speed differential along the surface of the cone at a given rotation. The intermediate ring is in contact with the cone along a line, not just at a distinct point. The point on that line which is closer to the large end of the cone is moving faster than the point at the smaller end. This causes the ring to twist. This tendency is further pronounced in the opposing cones model. The point on the drive shaft side small end is moving more slowly than the drive shaft side large end. The drive shaft side small end is opposite the driven shaft side large end which has more resistance in trying to cause the driven shaft to rotate, further pulling the ring out of its ideal plane. Henceforth, this phenomenon shall simply be referred to as the "twist problem".
The design of the power transfer mechanism must meet two contrary ideals. The ring or power transfer mechanism must be as wide as possible in order to achieve maximum traction, and must be as narrow as possible to minimize the twist problem and to facilitate the lateral movement needed for shifting.
A listing of prior art follows with a very short description of the invention. Each patent discloses a CVT either with two opposing cones or with a cone and a cylinder. Some disclose both types. Each has a belt, ring, or wheel (or a multiplicity of one of these three) as the power transfer element.
Evans (U.S. Pat. No. 390,216 October 1888, U.S. Pat. No. 627,491 June 1899, and U.S. Pat. No. 742,977 November 1903) teaches a device with two cones and a belt.
Halsey (U.S. Pat. No. 680,916 August 1901) teaches a cone and cylinder device with a ring.
Sparks (U.S. Pat. No. 1,055,677 March 1913) and Delacour (U.S. Pat. No. 1,191,771 July 1916) each teach a device with a wheel on a rod (variation of a ring on a cylinder) pressed against a cone.
Garrard (GB 298,676 October 1928) teaches a device with two cones and a ring.
Pourtier (U.S. Pat. No. 2,432,442 December 1947) discloses a two cone device with a ring surrounding each cone, each ring making a friction contact with its cone and the two rings transferring power from the one to the other by means of gearing.
Mikina (U.S. Pat. No. 2,583,790 January 1952) discloses a cone and cylinder device as well as one with two opposing cones, both versions using two power transfer elements.
Rohs (EP 878,641 November 1998 and later as U.S. Pat. No. 5,924,953) discloses two cone device in which the ring moves parallel to the shafts of the cones.
Each will be discussed later in greater depth to demonstrate in what manner the device previously disclosed is more bulky, more complicated in design, or less capable either of operating under a heavy load or of dealing with the twist phenomenon than the present invention.